In order to insure that multi-focal lenses and progressive power lenses that are capable of correcting astigmatism are manufactured in a rapid way in accordance with the directions that are specifically formulated for users by ophthalmologists or opticians, lens elements of various specifications are preliminarily prepared and, as soon as orders are received, they are combined in an appropriate way without grinding or polishing and bonded together to produce cemented lenses. This is a well known practice which may be implemented, e.g., by preliminarily preparing a front lens element (which is to be positioned on the object side) that provides power for the final lens and a rear lens element (which is to be positioned on the eye side) that provides the degree of astigmatism in diopters and the axis of astigmatism, and bonding these together to form a cemented lens according to specific directions. Before cementing, the individual lens elements are usually provided with a hard coating layer either on the side to become an outer surface or on both sides, and after optional tinting an anti-reflection film is formed to produce a complete cemented lens.
Plastic materials of which cemented lenses are made incorporate additives such as UV absorbers and antioxidants in order to improve the lightfastness of the lenses. Therefore, if UV-curable adhesives are used to cement lens elements together, UV radiation will not easily reach the area where the adhesive has been applied, and the adhesive will not be fully cured unless the dose of UV radiation is considerably increased. However, an excessive dose of UV radiation can cause adverse effects on the plastic lens material. On the other hand, if thermosetting adhesives are used to cement lens elements, they must be cured at comparatively low temperatures in order to insure that defects such as yellowing will not occur in the plastic lens material, but this has resulted in unduly prolonged cure times.